A nuclear fuel assembly for a boiling reactor comprises several vertical fuel rods arranged in sub-bundles. Individual vertical water-filled rods may be contained within each sub-bundle of the nuclear fuel assembly. The sub-bundles of fuel rods in the fuel assembly are separated from each other by a channel-formed supporting device of substantially cruciform cross-section.
From, for example, U.S. Pat. Nos. 4,478,786, 4,578,241 and 4,587,093, it is known to separate the sub-bundles with a channel-formed support member having a generally square cross-section. In the above-mentioned fuel assemblies with a substantially square cross-section, it has been found to be advantageous to separate the sub-bundles of the symmetrically arranged fuel rods by means of a cruciform support member connected at intervals to the wall of the fuel channel. In addition to improved reactive effects, when the channel-formed support member is filled with moderator water, this also provides an improved design from a strength point of view. Since the channel-formed support member is connected to the walls of the fuel channel, a light and sturdy design is obtained which is simple to manufacture.